That just sounds crazy Teila! I had enough dramas integrating 2 in and everyone else was getting along! Can't imagine it:/
It is meant to get above 40 degrees here today. I am so worried about the girls. My Sussex doesn't cope well at all with it and the feizzle isn't far behind. I have put out a frozen 2L bottle in the covered run for each of them as well as lunchbox ice bricks in the nest boxes and ice in the waterers. The bedding has been wet down and everyone is looking good at the moment. Anything else I should do??
Yeah, it is a bit on the crazy side smhoekzema, funnily enough, I had less dramas when I introduced LuLu (Frizzle) to the flock and she was a total newbie!
LuLu did not cope well the other week during the hot spell we had; might be a Frizzle-thing

Anyways, in addition to the above, if they have a favourite spot in the shade, either outside or in the run, maybe damp it down; I have learnt that they like to keep cool by laying in the damp earth. Also, satay (or is it Sam) has a sprinkler going in the run to help keep them cool. I have a mister set up for those extremely hot days.
Another couple of things to try are frozen vegies in water; Fancy reckons not only does it keep them cool, it takes their minds off the heat. I always have watermelon on hand for those hot days to aid with hydration.
Otherwise, just keep a close eye on them, which it sounds like you are doing, and frequent changes of water.
My gals do not like being wet but I have a friend on another thread and her Blue Cochin hen likes to stand in a bowl of water when it gets too hot ... I have asked her for photos

I hope all goes well for you and your chickens today.